Screen printing method

ABSTRACT

Screen printing apparatus and method for printing a design on a porous substrate by applying ink through a screen by means of a rotatable cylindrical squeegee which is provided with an improved peripheral porous resilient compressible cover made of reticulated open cell foam and in which the squeegee is rotated under compressive force in contact with the surface of the screen in the presence of a supply of ink so as to compress the peripheral layer against the surface of the screen to thereby increase the area of contact between the squeegee and the screen and to at least partially compress the pores in the area of contact whereby the peripheral porous cover envelops a portion of the ink so that a portion of the ink is first absorbed and as it enters the area of compressed contact with the screen it is then expelled from the open pores to thereby force the ink under pressure through the openings in the screen and into the substrate throughout the area of contact between the screen and the squeegee.

United States Patent [191 Lewicki, Jr.

1 Nov. 5, 1974 1 1 SCREEN PRINTING METHOD Walter J. Lewicki, Jr., Lancaster,

[73] Assignee: Armstrong Cork Company,

Lancaster, Pa.

[22] Filed: Sept. 17, 1973 [21] Appl. No; 397,676

Related US. Application Data [63] Continuation-impart of Ser. No. 93,183, Nov. 27,

1970, abandoned.

[75] Inventor:

[52] US. Cl 101/129, 101/120, 101/367 [51] Int. Cl B41m 1/12, B411 13/06 [58] Field of Search 101/120, 367, 129

[56] References Cited UNITED STATES PATENTS 2,419,695 4/1947 Shuttleworth et a1. 101/119 2,763,208. 9/1956 Rockoff et al 101/367 3,352,234 11/1967 Londahl et a1 101/120 X FOREIGN PATENTS OR APPLICATIONS 1,111,698 11/1955 France ..10l/l19 2,011,743 9/1971 Germany 101/120 Primary ExaminerClyde l. Coughenour 5 7 ABSTRACT Screen printing apparatus and method for printing a design on a porous substrate by applying ink through a screen by means of a rotatable cylindrical squeegee which is provided with an improved peripheral porous resilient compressible. cover made of reticulated open cell foam and in which the squeegee is rotated under compressive force in contact with the surface of the screen in the presence of a supply of ink so as to compress the peripheral layer against the surface of the screen to thereby increase the area of contact between the squeegee and the screen and to at least partially compress the pores in the area of contact whereby the peripheral porous cover envelops a portion of the ink so that a portion of the ink is first absorbed and as it enters the area of compressed contact with the screen it is then expelled from the open pores to thereby force the ink under pressure through the openings in the screen and into the substrate throughout the area of contact between the screen and the squeegee.

1 Claim, 1 Drawing Figure SCREEN PRINTING METHOD CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 93,183 of Walter J. Lewicki, .Ir., filed Nov. 27, 19700, now abandoned, for Compressible Magnet Rod for Rotary Screen Printing.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is directed to an apparatus and method for screen printing incorporating an improved squee gee structure having a porous peripheral layer and which is rotated against the screen under compressive force to provide improved printing.

2. Description of the Prior Art Screen printing apparatus having a rotary cylindrical metalpattern screen for engaging the substrate and provided with a rotary squeegee with a metal core and a non-porous, relatively hard or firm rubber covering rotating in engagement with the inner surface of the screen are known in the art. An example of such apparatus is shown in U.S. Pat. No. 3,216,349. Squeegees having felt covers and Squeegees with rubber covers formed with parallel grooves have also been used in connection with screen printing, as shown in U.S. Pat. Nos. 1,541,787 and 2,753,794.

The foregoing devices fail to obtain the advantages of the present invention in providing selectively greater speed of printing, greater depth of penetration, greater ink deposition, greater uniformity of ink application and greater control of speed and depth of printing.

Outside of the field of screen printing, U.S. Pat. No. 3,351,040 discloses a rubber sponge covered roller used for moistening stamps and other papers; U.S. Pat. No. 3,530,792 shows a porous foam printing pad or stamp for printing on ceramic material; and U.S. Pat. No. 2,763,208 shows a porous rubber-covered ink applying roller for applying ink to printing plates and types. However, these devices function quite differently from a squeegee in screen printing.

SUMMARY OF THE INVENTION The present invention provides, in the art of screen printing on porous substrates, an improved apparatus and method to provide selectively greater speed of printing, greater depth of penetration, greater ink deposition, greater uniformity of ink application and greater control of the speed and depth of printing. I have found that these and other advantages are obtained by providing a screen printing apparatus and method employing an improved squeegee having a porous comressible peripheral layer which is rotated under compressive force in contact with the screen to thereby increase the area of contact and to at least partially compress the pores in the area of contact and with an ink supply provided immediately adjacent to and in advance of the area of contact whereby the peripheral porous cover envelops a portion of the ink so that a portion of the ink is first absorbed and as it enters the compressed area of contact with the screen it is then expelled from the open pores to thereby force the ink under pressure through the openings in the screen and into the substrate substantially throughout the area of contact between the screen and squeegee.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing shows a partially diagrammatic crosssectional side view of a portion of a rotary screen printing apparatus embodying my invention and having a rotatable squeegee with a porous compressible resilient peripheral layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, there is shown a conventional screen printing apparatus 2, such as would be used on a Zimmer printer. The screen 4 is a rotary screen which is provided with a plurality of small holes defining the pattern to be printed. A rotatable squeegee 5 embodying a magnet rod 6 is utilized to force the ink through the small holes of the rotary screen onto a substrate 8 which is to be printed. A conventional printing blanket l0 backs up the substrate. A support table structure 12 is positioned below the printing blanket. Into the support table structure there is placed a magnet 14 which is operated by a magnet coil 16. The magnet operates upon the magnet rod 6 of squeegee 5 to force the squeegee against the rotary screen 4. Ink is supplied through an ink supply pipe 18. A reservoir of ink 20 is maintained in advance of the squeegee. This reservoir of ink provides a supply of ink which the squeegee may force down between the small holes of the screen 4 and into the substrate.

The squeegee 5 is rotated in a counterclockwise di- The squeegee 5 is formed of a central magnet rod 6 of suitable magnetic material and is surroundedby a porous resilient compressible cover 7. l have found that a magnet rod made of a solid steel cylindrical bar approximately one inch in diameter serves very satisfactorily. However, other magnetic material such as iron and various alloys thereof may also be employed and the specific diameter of the rod is not critical.

The porous, resilient, compressible cover may be made of any suitable resilient plastic or resin open cell foam which is unaffected by the ink employed, which has good wear characteristics and which has a pore size which will readily absorb the ink. I have found that very satisfactory inks for use with my process and apparatus are plastisol inks having a viscosity range of approximately 1,200 cps to 3,800 cps and the ink may be either thixotropic, pseudoplastic, or dilatant. With inks of this type, 1 have found that a reticulated, open cell polyurethane foam having 10 to 100 pores per inch, primarily 60 to pores per inch serves very satisfactorily. The thickness of'the cover may vary, but 1 have found that a thickness in excess of one-fourth inch, preferably approximately three-eighths inch, provides very satisfactory results. Typical foams uitable for use in my squeegee covers are disclosed in U.S. Pat. Nos. 3,425,890 and No. 3,025,200.

In a Zimmer printing apparatus the magnetic field strength in the coil 16 may be varied to vary the downward pressure of the squeegee against the screen. The Zimmer machine provides various settings for the magnetic field from 1 to 6 and these settings result in various magnetic field strengths varying approximately from 1 15 gauss to 1,300 gauss. The magnetic field strength is preferably adjusted in operation to cause the foam cover to compress to between approximately onethird and two-thirds of its original thickness at the center of the area of contact with the screen.

Various porous substrates may be printed by means of my improved method and apparatus. Thus, various fabrics, typically carpet fabrics, porous foams and porous floor covering materials may be printed by my apparatus and method.

In the utilization of my method and apparatus the porous substrate 8, blanket and table 12 are arranged in superposed relationship beneath the rotary screen 4 with the squeegee 5 in engagement with the inner surface of the screen at its area of contact with the substrate. The magnetic setting on the apparatus is adjusted to compress the porous resilient'cover to approximately one-third to two-thirds of its thickness and a supply of ink is fed through supply pipe 18 to provide a reservoir of ink 20 on the side of the squeegee towards which it rotates in operation. The substrate is then fed beneath the screen in a direction to the right as viewed in thE drawing and the screen and squeegee are rotated in a counterclockwise direction.

The compression vof the cover against the screen causes a flattening of the cover at the area of contact thus increasing the area of contact between the squeegee and screen. A greater volume of ink is thus pumped through the screen and into The substrate due to the fact that the peripheral porous layer envelops a portion of the ink whereby a portion of the ink is first absorbed and as it enters the compressed area of contact with the screen it is then expelled from the open pores, to thereby force the ink under pressure through the open ings in the screen and into the substrate substantially throughout the area of contact between the screen and squeegee.

l have found that by means of my improved method and apparatus 1 can obtain selectively greater depth of penetration, greater ink deposition, greater speed of operation, greater uniformity of ink application and greater control of the depth of penetration.

By increasing the speed offeed, the depth of penetration is reduced and decreasing the speed of feed results in greater depth of penetration. Greater uniformity and control can be obtained by adjusting the magnetic field strength and the resulting compression of the porous resilient cover. The following is a typical example of one embodiment of my invention.

EXAMPLE l The apparatus described above and shown in the drawing is provided with a squeegee having a one inch solid steel magnet rod covered with a reticulated open cell polyurethane foam approximately three-eighths inch thick and primarily between 60 and 80 pores per inch. A substrate approximately mils thick made of porous sintered polyvinyl chloride particle material is proximately 35 mils is obtained. By increasing the speed, the ink penetration was decreased. The product. resulting therefrom is useful, among other things, as a hard floor covering.

When the same operation was repeated utilizing a standard Zimmer magnet rod of a one inch diameter solid steel bar without any covering, an ink penetration of only 21 to 24 mils was obtained when the substrate was fed at 10 to 20 feet per minute.

The same operation was repeated utilizing a squeegee in the form of a solid steel rod having a non-porous compressible rubber covering approximately onefourth inch thick. At 10 feet per minute the penetration was 35 mils. However, at 20 feet per minute the ink penetration was only between 25 and 27 mils.

Thus, substantially greater depth of penetration is obtained by using my improved porous resilient compressible cover. In addition, l have found that l can obtain greater uniformity of penetration and better control.

EXAMPLE ll The following tests were conducted on Zimmer printing apparatus at magnetic settings No. 1 giving a flux density of 1 l5 gauss, No. 3 giving a flux density of 650 gauss and No. 6 giving a flux density of 1,300 gauss using three different types of Squeegees at different line speeds so as to show the different ink deposition and ink penetration obtained by the different types of Squeegees. In one set of tests, a squeegee of the standard Zimmer type consisting of a one inch diameter solid steel rod was employed. In a second set of tests, a squeegee consisting of a one inch diameter steel rod having a one-fourth inch thick covering of non-porous resilient rubberlike material was employed. A third set of tests were conducted with a squeegee such as taught in the present invention in the form of a one inch diameter steel rod covered with a three-eighths inch porous reticulated polyurethane foam having approximately pores per inch. Each of the tests was conducted with a similar substrate made of porous sintered polyvinylchloride approximately 42 mils thick. The ink employed in each case was a dilatant ink having a viscosity of 3,500 cps. With each type of squeegee, tests were conducted at line speeds of 12 feet per minute, 20 feet per minute and 40 feet per minute. The following table .shows the results obtained from these comparative tests.

Squeegee Magnetic Time Speed=l2 ft/min Time Speed=20 ft/min Time Sneed=40 ft/min Type Setting lnk Deposilnk Penetra lnk Deposilnk Penetralnk Deposilnk Penetration (grams/ tion (mils) tion tgrams/ tion (mils) tion (grams/ tion (mils) H H 911 911) H H 1" diameter solid 1 7.9 15 4.3 12 2.6 10 steel rod (Zimmer 3 9.2 II 5.0 18 3.] 14 type) a 10.1 23 6.0 20 3.9 16

1" diameter steel rod plus thick I 8.0 30 4.3 20 2.6 l5 nonporous resilient 3 9.4 33 4.9 23 3.0 l9 covering 6 l 1.0 35 6.] 26 4.0 16

Continued U Squeegee Magnetic Time Spced=l2 l't/min Time Sneed=2ll lt/min Time Snced=40 ft/min Type Setting lnk Deposilnk Penetralnk Dcposilnk Penetrul nk DCPOSI Ink Penetration (grams! tion (mils) tion (gr-ants] lion (mils) tron (grams! lion (mils) n n u n 1" diameter steel rod plus 94! thick I l3.7 36 10.5 7,4 24 X0 ppi reticulated open celled porous 3 I41] 39 1 L8 38 7.9 28 polyurethane foam covering 6 I41 42 Ill 8.6 30

From the foregoing table, it will be seen that the greatest ink deposition and ink penetration were obtained at each of the indicated line speeds by the use of the squeegee having the reticulated porous covering.

Thus, it will be seen that by means of my invention the objectives have been obtained in providing selectively greater speed of printing, greater depth of penetration, greater ink deposition, greater uniformity of ink application and greater control of speed and depth of printing.

1 claim:

l. The method of printing a design on a porous substrate by applying liquid ink through a screen having openings arranged in the desired design pattern which comprises:

arranging in superposed relationship the afore-said substrate and screen and arranging in superposed relationship to the screen a rotatable cylindrical squeegee surrounded by a peripheral porous resilient compressible layer at least one-fourth inch in thickness made of reticulated open cell foam: rotating the screen on the substrate while rotating'the squeegee in contact with the upper surface of the screen and simultaneously applying compressive force between the squeegee and the screen so as to compress the peripheral porous layer against the upper surface of the screen to thereby compress the porous layer to between approximately onethird and two-thirds of its normal thickness and to increase the area of contact and to at least partially compress the pores in the area of contact; and

providing a supply of liquid ink at and adjacent in adsqueegee. 

1. The method of printing a design on a porous substrate by applying liquid ink through a screen having openings arranged in the desired design pattern which comprises: arranging in superposed relationship the afore-said substrate and screen and arranging in superposed relationship to the screen a rotatable cylindrical squeegee surrounded by a peripheral porous resilient compressible layer at least onefourth inch in thickness made of reticulated open cell foam: rotating the screen on the substraTe while rotating the squeegee in contact with the upper surface of the screen and simultaneously applying compressive force between the squeegee and the screen so as to compress the peripheral porous layer against the upper surface of the screen to thereby compress the porous layer to between approximately one-third and two-thirds of its normal thickness and to increase the area of contact and to at least partially compress the pores in the area of contact; and providing a supply of liquid ink at and adjacent in advance to the area of engagement between the screen and squeegee whereby the peripheral porous layer envelops a portion of the liquid ink so that in a continuous manner a portion of the liquid ink is first absorbed and as it enters the area of compressed contact with the screen it is then expelled from the open pores to thereby force the liquid ink under pressure through the openings in the screen and into the substrate substantially throughout the area of contact between the screen and squeegee. 